Dark or black stool is usually caused by something you ate, drank, or took as a supplement. Iron pills, bismuth-based medications like Pepto-Bismol, and certain foods are the most common culprits. Less often, dark stool signals bleeding in the upper digestive tract, which requires prompt medical attention. The key is knowing how to tell the difference.
Foods That Turn Stool Dark
Several everyday foods can make your stool noticeably darker. Blueberries, black licorice, and blood sausage are well-known offenders. The dark pigments in these foods pass through your digestive system mostly intact, coloring your stool along the way. Beets can also darken stool, sometimes adding a reddish tint that looks alarming but is harmless.
Food-related color changes typically show up within a day or two of eating the food and resolve just as quickly once you stop. The stool looks darker than usual but keeps its normal consistency and doesn’t have an unusually strong or foul smell. If you recently ate any of these foods, that’s likely your answer.
Medications and Supplements
Iron supplements are one of the most common non-food causes of black stool. If you’ve recently started taking iron tablets for anemia or as part of a prenatal vitamin, expect your stool to turn dark green or black. This is normal and not a reason to stop taking them.
Bismuth subsalicylate, the active ingredient in Pepto-Bismol and similar products, also turns stool jet black. This happens because bismuth reacts with hydrogen sulfide gas naturally present in your gut, forming a compound called bismuth sulfide, which is intensely black. The effect can last several days after your last dose. Activated charcoal, sometimes taken for digestive issues or as part of detox products, does the same thing.
When Dark Stool Means Bleeding
Dark, tarry stool that hasn’t been explained by food or medication could be melena, a sign of bleeding somewhere in the upper digestive tract (esophagus, stomach, or the first part of the small intestine). Blood that travels through the full length of the digestive system gets broken down by stomach acid and bacteria, turning it black and giving the stool a distinctive tar-like appearance.
Melena looks and feels different from food-related dark stool. It tends to be sticky, almost like tar, and has a noticeably strong, unpleasant odor. It only takes about 100 to 200 milliliters of blood in the digestive tract to produce visible melena, roughly half a cup or less.
The most common medical causes include:
- Peptic ulcers: open sores in the stomach lining or upper small intestine, often accompanied by burning abdominal pain
- Gastritis: inflammation of the stomach lining, which can cause upper abdominal pain or nausea
- Esophageal varices: swollen veins in the esophagus, most often seen in people with liver disease
- Tears in the esophagus: sometimes caused by severe or prolonged vomiting
How to Tell the Difference
Start by thinking about what you’ve consumed in the last 48 hours. If you took Pepto-Bismol, iron pills, activated charcoal, or ate a handful of blueberries, you almost certainly have your explanation. The stool will be dark but otherwise look and feel normal.
Melena from bleeding has a tarry texture and stickiness that’s hard to miss. People who’ve experienced it often describe it as unmistakable. It also tends to come with other symptoms: abdominal pain, nausea, feeling lightheaded, or general weakness. If you haven’t taken any of the common supplements or foods and the dark stool persists for more than a day or two, bleeding is worth considering.
Symptoms That Signal an Emergency
Certain symptoms alongside dark stool mean you should get to urgent care or an emergency room:
- Vomiting blood or vomit that looks like coffee grounds
- Dizziness, weakness, or lightheadedness, which can indicate significant blood loss
- Heart palpitations or shortness of breath
- Several consecutive days of black, tarry stool
Abdominal pain paired with dark stool can point to a stomach ulcer or gastritis. Chest pain may suggest the bleeding is coming from the esophagus. Back pain or upper abdominal pain can sometimes indicate a pancreatic issue. Any of these combinations warrants medical evaluation, typically with an endoscopy (a camera passed through the mouth to view the upper digestive tract) performed within 24 hours of presentation.
Dark Stool in Babies
Newborns pass very dark, greenish-black stool called meconium during their first few days of life. This is completely normal. It’s the result of everything the baby swallowed in the womb: amniotic fluid, mucus, bile, and shed cells. It clears within a few days as the baby begins feeding.
After those first few days, dark stool in a baby has different implications. Iron-fortified formula commonly produces thick, dark green or black stool that looks alarming but is harmless. However, if a baby older than three days passes tar-like black stool that isn’t explained by iron supplementation, it could indicate blood has entered the gastrointestinal tract and needs medical evaluation.